1. Technical Field
The present invention relates generally to torsional resonance frequency measuring devices and methods applied to rotating members, and more particularly, to a device and method that measures the torsional resonance frequency of a rotating member supported in an unrestrained free-free drive-chain through impact excitation by using a machine-side converter.
2. Description of Related Art
In recent years, due to the depletion of fossil fuel and environment concerns, a lot of countries have focused on developing wind power generation. In order to generate electric power, the wind turbines have rotating blades driven by the wind, which convert the wind power to the mechanical power, and the mechanical power is then converted into electrical energy by an electrical generator, and finally, the electrical energy is transformed into an appropriate form by a power converter and fed to loads such as road lights, energy storage devices such as batteries, or a power transmission and distribution system. Generally, wind turbines that feed electrical energy to loads and energy storage devices are described as non grid-tied wind turbines and wind turbines that feed electrical energy to power transmission and distribution systems are described as grid-tied wind turbines. Most of the current large-scale wind turbines are grid-tied wind turbines.
Since wind turbines in operation must bear wind loads with randomness and turbulence, they are often subject to vibration and noise problems. When rotational machines are applied to large-scale power generators or traction motor equipments (such as large power grid-tied wind turbines), torsional vibration along the drive-chain is a major factor causing element damage and noise. Therefore, how to suppress vibration and noise of wind turbines has become an important topic.
In view of the above potential problems, the torsional resonance frequency of a wind turbine should be obtained for determining the operation state of the wind turbine. There are various torsional resonance frequency measuring methods and devices in the art. Generally, two ends of a transmission shaft (rotor) for a wind turbine are supported in an unrestrained free-free manner during normal operation. The torsional resonance frequency of such a wind turbine is usually measured through impact excitation, torsional shaker excitation, running at variable frequencies and so on, wherein the method of impact excitation is very simple and rapid and is most widely used.
FIG. 1 is a diagram showing the conventional impact excitation method for measuring the torsional resonance frequency of a drive-chain. Referring to FIG. 1, the method uses a signal analyzer 1, an accelerometer 2 and a hammer 3. To measure the torsional resonance frequency of a drive-chain, a transmission shaft 5 of a permanent magnet synchronous generator (PMSG) is struck by the hammer 3 to generate impulse torque, and vibration signals are picked up by the accelerometer 2, and signals outputted from the hammer 3 and the accelerometer 2 are sampled and calculated through the signal analyzer 1 to find the torsion resonance frequency of the drive-chain.
However, there are some drawbacks in using such an impact excitation method. For example, in the measurement of the drive-chains of the wind turbines, precision inspection instruments and measuring tools, such as the accelerometer and the hammer, need to be transported or carried by maintenance staff to the site where a wind turbine is located, and the transmission shaft of a power generator needs to be hit by the hammer to generate impulse torque. However, since large-scale wind turbines are usually installed at higher places, and most of the wind turbines or wind capturing devices are generally installed on remote mountains, seaside or even offshore islands for achieving preferred wind capture effect and avoiding noise pollution, to make on-site measurement results in high cost and wasting of time. Further, wind turbines high above the ground pose a potential safety risk to on-site maintenance staff.
Therefore, it is worthwhile to provide a torsional resonance frequency measuring device and method with high efficiency, high safety and low cost.